Method of coating paper



Aug. 25, 1964 w. R. TURNER 3,145,121

METHOD OF comma PAPER Filed Aug. 10, 1962 PAPER OR PAPERBOARD SATURATED CARBOXYLIC ACID PRETREATING V (4 f0 l8 CARBON STEP ATOMS) AND TRIFLUOROACETIC ACID WATER WASH ETHYL ALCOHOL WASH DRY

COATING STEP MOLTEN WAX WAX COATED PAPER OR PAPERBOARD WILLIAM R. TURNER IN VEN TOR MJM ATTORNEY United States Patent 3,146,121 METHOD GF C(JATIN G PAPER William R. Turner, Drexel Hill, Pa., assignor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Aug. 10, 1962, Ser. No. 216,061 Claims. (Cl. 117-60) This invention relates to a method for coating paper and paperboard and, more particularly, to a method for coating paper and paperboard with wax to produce a coated product having improved properties.

It is well known that waxes, particularly petroleum waxes, are excellent waterproofing agents. However, since these waxes are hydrophobic materials, they tend not to coat or saturate paper or paperboard thoroughly due to the hydrophilic nature of the paper. Thus adhesion of Wax to paper to render the same completely waterproof is difiicult to accomplish. In attempting to coat a paper which is rough or possesses standing fibers as a result of folding, creasing, or scoring, a thin-surface coating of wax would not cover the individual fibers completely and thus leave unprotected wicks through which aqueous liquids could spread into the paper web. Thus adhesion of wax to paper and paperboard to completely coat the same and render them waterproof are perennial problems with regard to the coating of paper food containers.

A method now has been found whereby paper or paperboard may be coated with wax in such a way so as to overcome inherent prior art disadvantages of coating processes. This method comprises pre-treating the surface of the paper with a carboxylic acid in the presence of trifluoroacetic anhydride and thereafter applying a wax coating to the pre-treated material.

It is therefore an object of this invention to provide an improved method for coating paper and paperboard.

It is another object of this invention to provide a method for coating paper and paperboard with wax whereby the wax tends to penetrate into the paper and thus render the paper more completely liquidproof and more flexible.

Other objects will be apparent from the following description and claims.

Briefly stated, the method of this invention comprises first treating the surface of a cellulosic paper or paperboard With a small amount of a carboxylic acid in the presence of trifluoroacetic anhydride and thereafter coating the treated paper with a wax and subsequently recovering a wax-coated paper product.

The drawing contains a flowdiagram of the method of the invention.

The wax used in this invention may be an animal, vegetable, mineral, or synthetic Wax or mixtures thereof. Examples of waxes which may be used in this invention are beeswax, carnauba, palm, ouricury, rafiia, candililla, Madagascar, sugar cane wax, bamboo leaf wax, Esparto, Japan, Paraflint, cranberry wax, ozocerite, montan, and ceresin; petroleum waxes, i.e., paraffin and microcrystalline Waxes, are preferred, paraffin Waxes being most preferred. It will be understood, however, that any wax which has a melting point lower than ambient temperatures cannot be used for obvious reasons. The wax, therefore, should melt at a temperature not less than about 120 F. nor should it exhibit any appreciable cold flow properties at temperatures less than about 120 F. It is most preferred in this invention to use a paraffin wax having a melting point of from about 120 F. to about 170 F.

The carboxylic acids to be used in treating the paper are saturated unsubstituted carboxylic acids containing from 4 to 18 carbon atoms, preferably from 6 to 10 carbon atoms. Examples of suitable saturated unsubstituted ice carboxylic acids which may be used to pre-treat the paper include butyric, valeric, hexanoic, enanthic acid, caprylic acid, pelargonic acid, decanoic acid, lauric acid, myristic acid, tetradecanoic acid, palrnitic acid, and stearic acid.

The amount of carboxylic acid to be used in pre-treating the paper may vary from 1.0 gram of acid per 3.0 grams of paper to about 20.0 grams of acid per 1.0 gram of paper. It is most preferred in the practice of this invention to use about 1.0 gram of acid per 1.0 gram of paper to about 10.0 grams of acid per 1.0 gram of paper.

The pre-treatment of the paper with the carboxylic acid is done in the presence of trifluoroacetic anhydride. The amount of trifluoroacetic anhydride to be used compared to the amount of acid to be used will vary from about 0.5 gram of anhydride per 1.0 gram of acid to about 10.0 grams of anhydride per 1.0 part of acid, preferably from about 0.5 gram of anhydride to 1.0 gram of acid to about 5.0 grams of anhydride to 1.0 gram of acid.

The time of treatment of the paper with the carboxylic acid-trifluoroacetic anhydride mixture may vary from about 10 minutes to about 4 hours, preferably from about 30 minutes to about 1 hour.

The following example will serve to further illustrate certain preferred specific embodiments of the instant invention.

EXAMPLE I Separate samples of a commercial paperboard, having a caliper of 24 mils and a densometer of 52 seconds per cc. of air, was treated with different saturated carboxylic acids in the presence of trifluoroacetic anhydride for 30 minutes. Upon completion of the pre-treatment, all samples were washed thoroughly with water and any free acid remaining thereon was removed by washing with ethyl alcohol. All samples were air dried; and 4 of the samples were immersion-coated by dipping for 10 seconds, and 4 of the samples were immersion-coated by dipping for 30 seconds in a paraflin wax having a melting point of from F. to 124 F. The results obtained are shown in the table.

Table Immer- Percent Sam- Wt. of Wt. of Wt. of sion Wax ple paper TFA, Acid acid time penetra- No. (gms.) (gms.) (gms.) (sec) tion into paper 3 10 15 3 30 20 3 12 10 10 3 12 30 30 3 12 Butyric 3. 3 10 35 3 12 3.3 30 90 3 12 Caproic 4. 3 10 60 3 12 o 4.3 30 80 3 12 Caprylic 5. 4 10 7O 3 12 do 5.4 30 80 3 12 Stearrc 10. 7 10 20 3 12 o 10.7 30 75 *Trifluoroacetic anhydride.

It is apparent from the data shown in the table that the wax coating on an untreated paperboard or paperboard treated only with trifluoroacetic anhydride tends to stay on the surface of the board and does not penetrate the board to any great extent (see Sample Nos. 1, 2, 3, and 4). In those instances where a wax coating does not penetrate into a paper or paperboard, it is well known that such coatings have a tendency to crack quite readily when creased or flexed. It will be noted further from the data shown in the table that the wax coatings penetrate into the paperboard to a much greater extent when using the method of this invention (see Sample Nos. 5 to 12). It is also apparent that the degree of penetration of the wax into the paperboard coated according to the method of this invention is superior when the carboxylic acid used in the pre-treatment of the board contains from about 6 to about 10 carbon atoms (compare Sample Nos. 5, 6, 11, and 12 with 7, 8, 9, and 10). Since it is well known in the art that the greater the penetration of a wax coating into the material to be coated, the more waterproof will be the coated material, it is apparent that the coated materials produced according to the process of this invention are not only superior with regard to flexibility characteristics but also with regard to liquid repellency.

Thus many modifications and variations of the invention herein described may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method of coating paper and paperboard which comprises pre-treating the paper and paperboard with a mixture of a saturated carboxylic acid having from 4 to 18 carbon atoms in the molecule and trifiuoroacetic anhydride, said carboxylic acid ranging from 1.0 gram of carboxylic acid per 3 grams of paper to 20.0 grams of carboxylic acid per 1.0 gram of paper, said trifluoroacetic anhydride ranging from 0.5 to 10.0 grams of trifluoroacetic anhydride per gram of said carboxylic acid used, drying the pre-treated paper, coating the pre-treated paper with a molten wax having a melting point not less than about 120 F. and recovering the wax-coated product.

2. A method of coating paper and paperboard which comprises pre-treating the paper and paperboard with a mixture of a saturated carboxylic acid having from 4 to 18 carbon atoms in the molecule and trifiuoroacetic anhydride, said carboxylic acid ranging from 1.0 gram of carboxylic acid per 1.0 gram of paper to 10.0 grams of carboxylic acid per 1.0 gram of paper, said trifluoroacetic anhydride ranging from 0.5 gram to 5.0 grams of trifluoroacetic anhydride per gram of said carboxylic acid used, drying the pretreated paper, coating the pretreated paper with a molten wax having a melting point not less than about F. and recovering the wax-coated product.

3. A method in accordance with claim 2 wherein the carboxylic acid contains from 6 to 10 carbon atoms.

4. A method in accordance with claim 2 wherein the wax is a paralfin wax.

5. A method in accordance with claim 2 wherein the wax is a microcrystalline wax.

6. A method in accordance with claim 2 wherein the wax is a mixture of paraffin and microcrystalline waxes.

7. A method in accordance with claim 2 wherein the Wax is a synthetic wax.

8. A method in accordance with claim 2 wherein the Wax is a natural wax.

9. A method in accordance with claim 2 wherein the carboxylic acid is caproic acid.

10. A method in accordance with claim 2 wherein the carboxylic acid is caprylic acid.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF COATING PAPER AND PAPERBOARD WHICH COMPRISES PRE-TREATING THE PAPER AND PAPERBOARD WITH A MIXTURE OF A SATURATED CABOXYLIC ACID HAVING FROM 4 TO 18 CARBON ATOMS IN THE MOLECULE AND TRIFLUOROACETIC ANHYDRIDE, SAID CARBOXYLIC ACID RANGING FROM 1.0 GRAM OF CARBOXYLIC ACID PER 3 GRAMS OF PAPER TO 20.0 GRAMS OF CARBOXYLIC ACID PER 1.0 GRAM OF PAPER, SAID TRIFLUOROACETIC ANHYDRIDE RANGING FROM 0.5 TO 10.0 GRAMS OF TRIFLUROOACETIC ANHYDRIDE PER GRAM OF SAID CARBOXYLIC ACID USED, DRYING THE PRE-TREATED PAPER, COATING THE PRE-TREATED PAPER WITH A MOLTEN WAX HAVING A MELTING POINT NOT LESS THAN ABOUT 120*F. AND RECOVERING THE WAX-COATED PRODUCT. 